Tri-frequency instrumentation antenna

ABSTRACT

The tri-frequency antenna is a multi-frequency antenna providing isolation between different frequency bands and an impedance match for all frequencies involved. It is ideally suited for use on spinning missiles because of its roll-symmetrical antenna pattern. It may be used as a combination transmitting and receiving antenna without danger of ionization at high altitudes with reasonable radiation power levels. In missiles, the missile outer surface serves as the antenna radiating elements. Associated matching networks and a common coupler allows both isolation and matching.

United States Patent [191 Howell et al.

TRl-FREQUENCY INSTRUMENTATION ANTENNA Inventors: James Howell; Wayne T. Hudson;

Henry A.. Krzyzewski, all of Huntsville, Ala.

The United States of America as represented by the Secretary of the Army, Washington, DC.

Filed: Feb. 28, 1973 App]. No.: 336,662

Assignee:

US. Cl 343/852, 343/858, 343/860 Int. Cl. H0lq 1/50 Field of Search 343/860, 852, 858, 705,

References Cited UNITED STATES PATENTS 10/1973 Leidy et al 343/802 [451 May 21, 1974 Primary Examiner lames W. Lawrence Assistant Examiner-T. N. Grigsby Attorney, Agent, or Firm-Edward J. Kelly; Jack W.

Voight ABSTRACT with reasonable radiation power levels. In missiles, the,

missile outer surface serves as the antenna radiating elements. Associated matching networks and a common coupler allows bothlisolation and matching.

5 Claims, 3 Drawing Figures mEml-inm 21 ISW 3812.494

sum 1 or 2 PATENTEDMAY 21 m4 SHEEI 2 BF 2 TO TRANS.-

REC. cm'cun FIG. 3

. 1 TRI-FREQUENCY INSTRUMENTATION ANTENNA BACKGROUND OF THE INVENTION In maintaining track of a missile, doppler shift frequencies allows tracking measurement to be obtained through well established methods. Doppler velocity and position, DOVAP, is a tracking system whereby a missile transponder transmits a preselected frequency to ground receiving stations in response to a signal from the ground stations. The signal from the missile may be a known multiple or sub-mutiple of the signal from ground stations allowing the signal received by ground stations to be compared with the transmitted signal to obtain velocity and position information therefrom.

Various types of DOVAP antennas such as top loaded stubs or cavity types have been used on missiles. However, these types of antennas do not yield a roll symetrical antenna pattern (toroidal) around the missile which is needed on spinning missiles to maintain signal continuity. Neither will theyhandle simultaneously a higher telemetry frequency. Typical weaknesses inherent in these and other DOVAP antenna systems include inability to handle both DOVAP and telemetry frequencies, ionization at high altitude, inefficient, mismatch between related frequencies, and radiation of rf energy within the missile resulting in interference with guidance electronics.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified diagrammatic drawing of a missile nose section embodying the invention with extraneous structure omitted.

FIG. 2 is a simplified schematic of the matching and isolation network for filtering respective doppler frequencies.

FIG. 3 is a single line diagram of the matching and isolation network at telemetry frequencies.

DESCRIPTION OF THE PREFERRED EMBODIMENT The tri-frequency instrumentation antenna allows operation at two preselected DOVAP frequencies and also at a. higher telemetry frequency. Typically, but not limited thereto, telemetry may be in the P or S band. The antennadoes not ionize at higher altitudes within the system power requirements and is matched for all three frequencies. The antenna structure prevents radio frequency (rf) energy from being radiated within the missile housing. Isolation is provided between the receive and transmit DOVAP ports of the antenna and the DOVAP or doppler frequencies are isolated from telemetry frequencies.

Referring now to the drawings wherein like numbers represent like parts in each of the several figures, FIG.

l discloses a preferred embodiment of the trifrequency instrumentation antenna. The nose cone or nose section of a missile is shown disposed for housing pertinent structure of the antenna system whereby the housing outer surface or skin functions as the antenna radiating elements I2, 14, and 16. These radiating elements are physically separated by nonconductive sections 18. Mounted within housing section 12 is a matching and isolation network for coupling transmitted and received doppler frequencies to the radiating elements. This energy is coupled through coaxial cables from respective connectors 22 and 24. An antenna feed pin 26 is substantially aligned along the longitudinal axis of the missile nose tip and is coaxially coupled to matching and isolation network 20. Matching network20 is shown housed in an airtight compartment 28 in the outer skin section 12. Compartment 28 may be pressurized to prevent ionization at high altitudes. A non-conductive bushing 30 insulates feed pin 26 from the inner surface of housing 28. The feed pin projects through the chamber emcompassed by non-conductive section 18a and is terminated on a conductive structural member 32. A coaxial cable coil 34 is disposed around feed pin 26. Coaxial coil 34 is supported by a non-conductive coil form 36 having electrically conductive end members 37 and 38 respectively joined to conductor surface 39 of structural member 32 and conductive surface 40 of structural member 28. One end of the coaxial coil 34 is terminated in a coaxial connector 42 for coupling energy through cable section 44 and coaxial connector 46 to appropriate telemetering transmitter or receiver equipment within additional missile housing (not shown). Similarly, the other end of coaxial coil 34 is coupled to a coaxial connector 48 for coaxial coupling to a matching and isolation network 50 for providing system telemetry information. Matching network 50 is housed under missile skin section 14 and is coaxially coupled to a telemetry feed pin 52. Feed pin 52 is coupled to missile skin surface 16 for radiating and receiving telemetry signals therefrom. Surface 16 comprises a quarter wave stub antenna tuned to the preselected telemetry frequency. The housing area around telemetry feed pin 52 and related support structure may be filled with an insulating foam as is well known in the art for preventing ionization at higher altitudes. Obviously well known in the art, the methods of structurally coupling and electrically cojpling between specific components is well known in the art and is not deemed pertinent to this disclosure and therefore not set forth herein.

FIG. 2 discloses the matching and isolation network 20 for the doppler velocity and position circuitry. An input-output junction allows coupling between network 20 and feed pin 26. One side of junction 60 is connected to an inductor L2 and a capacitor C2 connected as a tank circuit. The other side of the isolation tank circuit is connected to a matching L section comprising a series inductor L1 and a variable capacitor C1 connected between the inductor L1 and a circuit common. The matching L section is terminated across the coaxial connector 22 for coupling to the related doppler transmitter circuitry. Similarly the other side of junction 60 is coupled to an isolation tank circuit formed by inductor L3 and variable capacitor C3. The other side of tank circuit L3-C3 is coupled through a serially connected capacitor C4 and inductor L4 to the inner terminal of coaxial connector 24 for coupling to 3 external doppler receiver circuitry. The junction between L4 and C4 is connected through a variable ca pacitor C to the circuit common. L4 and C5 form a matching L filter section for the receiver circuitry.

L2 and C2 are tuned to F1, the receiver frequency, and therefore offer a very high or open circuit impedance at this frequency, preventing F1 from being'coupled into the transmitter circuit. At F2, the transmitter frequency, the series impedance of this tank circuit looks capacitive. Since this tank circuit is connected to the DOVAP feed pin which also looks capacitive at F2, the impedance looking into tank circuit L2C2 is capacitive. Thus, part of L1 is used as a series inductance to make this capactive impedance look resistive for matching with an L section filter. L1 is additionally used in co njuction with C1 to form the L section filter matching network on the F2 side, thereby matching the antenna to 50 ohms characteristic impedance at this frequency. Similarly, L3 and C3 are tuned to F2, offering a high series impedance or open circuit at this frequency. Thus the tank circuit L3-C3 prevents F2 from being coupled into the receiver circuit. At the receiver frequency (Fl) the impedance of L3-C3 appears inductive. At the receiver frequency DOVAP feed pin 26 also appears inductive, thus, the impedance looking into this tank circuit appears inductive. C4 is in series with this inductive impedance and is adjusted until the circuit appears resistive for matching with an L section matching circuit, L4 and C5 form the L section matching circuit for the receiver frequency, Fl, matching the antenna to 50 ohms characteristic impedance at this frequency.

In exciting the antenna radiating elements 12 and 14, energy at F1 and F2 is coupled through feed pin 26 to the radiating elements. The outer conductor of coaxial cable 34 functions as an rf choke coil and is connected in common with the bulk heads or housing immediately above and below the coil on surfaces 39 and 40. This choke coil allows the telemetry signal on the inner conductor of the coax to pass through the doppler antenna gap without interfering with or mixing with the DOVAP portion of the antenna. The impedance of the rf choke coil is high at DOVAP frequencies and therefore does not short out the antenna gap. Due to its short length the impedance of the DOVAP antenna is capacitive as measured at the feed pin without the if choke coil. Thus the number of turns on the rf choke coil is adjusted until the impedance measured at the feed pin is capacitive for the transmitter frequency F2 and inductive for the receiver frequency F 1,

FIG. 3 is a single line drawing of the circuitry between the telemetry antenna surface 16 and coaxial coil 34 inner conductor. Antenna stub 16, isolated from the remainder of the missile body by structure I 76, which maybe of any convenient length, for coupling the matching network to coaxial connector 48. A shorted stub 78 is joined as a branch to the transmission line at the junction of cable 74 and 76. Cable 70 is of a length to provide a resistive impedance at the telemetry frequency ofv operation. Thisparticular length is a function of the frequency used and is determined by well known means in conjunction with the impedance of the stub antenna. The resistive impedance of cable is then matched to the 50 ohm characteristic impedance by quarter-wave transformer 72. The characteristic impedance (Z' of the quarter-wave transformer is calculated to accomplish the matching. The length of shorted stub 78 is preselected to provide a quarterwave length at the telemetry frequency band of operation. Thus, the stub appears as an open circuit at these frequencies and does not interfere with the operation of the antenna at telemetry frequencies. The length of cable 74 is specifically adjusted so that the total distance from the stub short 79 to the telemetry band stub antenna 16 is one-half wavelength at F l and a wavelength at F2. This effectively places a short circuit across the telemetry band antenna gap at these frequencies so that the stub antenna 16 can function as part of the DOVAP antenna at Fll and F2 without interfering with the telemetry transmission.

In operating the telemetry circuit, incoming telemetry signals are coupled through stub antenna 16 and quarter-wave transformer 72 to the inner conductor of coaxial coil 34. The telemetry signal is carried within the small coaxial cable across the DOVAP antenna feed gap andis shielded by the coax outer conductor, thereby preventing interference with the DOVAP portion of the antenna. The other side of the r fchoke, coaxial cable coil 34, is connected through connectors 42 and 46 to the telemetering transmitter or receiver unit of the missile system. In operating the doppler transmitter-receiver system a signal'transmitted from the missole toward the ground station is coupled through matching and isolation network 20 to feed pin 26 .where it is developed across bulk heads 39 and 40, thereby developing the signals across radiating elements l2, l4, and 16. Any feedback of the doppler frequency through the inner conductors of elements 70, 72 and 74 is short circuited by shorted stub 78, thereby preventing the doppler frequencies from feeding back into the telemetry circuit. Received doppler frequencies impinging on the missile skin are transmitted through the system and into the missile receiver in a similar manner.

The impedance of the DOVAP portion of the antenna is independent of the impedance of the transmitter or receiver connected to the telemetry band portion of the antenna. Obviously if spacing is critical the matching and isolation box 20 may be mounted elsewhere in the missile structure and connected to feed pin 26 with coaxial cable of half-wavelength multiples of F1, since impedances on coaxial cables repeat themselves at half-wavelength intervals. For typical operation the telemetry frequency band may be P-band with the doppler velocity and position frequencies in a band approximately an order of 10 less than P-band, with F2 2F 1. The shorted stub behaves as an open circuit on the line for P-band frequencies and as a short circuit for the doppler frequencies. The rf choke 34 in the DOVAP cavity provides a means of signal flow without disturbing the DOVAP antenna since it looks like a high inductive reactance at frequencies Fll and F2.

Although a particular embodiment and form of this invention has been illustrated, it is apparent that various modifications and embodiments in the invention may be made by those skilled in the art without depart- 7 ing from the scope and spirit of the foregoing disclosure. Accordingly, the scope of the invention should be limited only by the claims appended hereto.

We claim:

1. A tri-frequency instrumentation antenna comprising: first and second frequency radiating and receiving members; impedance matching and isolation means having an input-output junction, an input junction, and an output junction, said input and output junctions being disposed for receiving doppler radar frequency energy for transmission and reception; coupling means connecting said input-output junction to said radiating and receiving members for coupling radiant energy therebetween; a high frequency band matching network having an input coupled to said coupling means and an output coupled to said second frequency radiating and receiving member for coupling preselected said coaxial cable coil being terminated across said first and second radiating members for controlling the reactance of the antenna; and the inner conductor of said coaxial coil having one end connected as said input to said band matching network and the other end disposed for carrying high frequency radiant energy thereto independent of energy coupled through said feed pin.

2. An instrumentation antenna as set forth in claim 1 and further comprising a coil form for supporting said coaxial cable coil around the axis of said feed pin; said coil form being a cylindrical non-conductive member having first and second electrically-conductive, apertured end members for terminating said coaxial cable shield conductor thereon and across said first and second radiating members respectively.

3. An instrumentation antenna as set forth in claim 2 wherein said matching and isolation means comprises first and second isolation tank circuits connected to said input-output junction; a first matching L filter section connected between said first tank circuit and said input junction for coupling input energy from said junction through said first tank circuit to said input-output junction; and a second matching L filter section connected between said second tank circuit and said output junction.

4. An instrumentation antenna as set forth in claim 3 wherein said band matching network comprises a quarter-wave transformer and coaxial cable serially connected between said second radiating member and said coaxial coil inner conductor for providing characteristic impedance matching therebetween, and a quarter-wave stub tuner connected between said quarterwave transformer and said coaxial coil inner conductor for providinga short-circuit terminal at said doppler radar frequencies and thereby preventing said doppler frequencies from impinging on said coaxial coil inner conductor.

5. An antenna as set forth in claim 4 wherein said first and second frequency radiating and receiving members comprise a housing assembly encompassing said matching and isolation means, said coupling means, and said band matching network; said first and second radiating members being joined together by a nonconductive support member. 

1. A tri-frequency instrumentation antenna comprising: first and second frequency radiating and receiving members; impedance matching and isolation means having an input-output junction, an input junction, and an output junction, said input and output junctions being disposed for receiving doppler radar frequency energy for transmission and reception; coupling means connecting said input-output junction to said radiating and receiving members for coupling radiant energy therebetween; a high frequency band matching network having an input coupled to said coupling means and an output coupled to said second frequency radiating and receiving member for coupling preselected high frequency energy therebetween; and wherein said coupling means is an antenna feed pin coupled to said first and second radiating members for coupling energy thereto, and a coaxial cable formed in a coil emcomPassing said feed pin, the outer conductive shield of said coaxial cable coil being terminated across said first and second radiating members for controlling the reactance of the antenna; and the inner conductor of said coaxial coil having one end connected as said input to said band matching network and the other end disposed for carrying high frequency radiant energy thereto independent of energy coupled through said feed pin.
 2. An instrumentation antenna as set forth in claim 1 and further comprising a coil form for supporting said coaxial cable coil around the axis of said feed pin; said coil form being a cylindrical non-conductive member having first and second electrically conductive, apertured end members for terminating said coaxial cable shield conductor thereon and across said first and second radiating members respectively.
 3. An instrumentation antenna as set forth in claim 2 wherein said matching and isolation means comprises first and second isolation tank circuits connected to said input-output junction; a first matching L filter section connected between said first tank circuit and said input junction for coupling input energy from said junction through said first tank circuit to said input-output junction; and a second matching L filter section connected between said second tank circuit and said output junction.
 4. An instrumentation antenna as set forth in claim 3 wherein said band matching network comprises a quarter-wave transformer and coaxial cable serially connected between said second radiating member and said coaxial coil inner conductor for providing characteristic impedance matching therebetween, and a quarter-wave stub tuner connected between said quarter-wave transformer and said coaxial coil inner conductor for providing a short-circuit terminal at said doppler radar frequencies and thereby preventing said doppler frequencies from impinging on said coaxial coil inner conductor.
 5. An antenna as set forth in claim 4 wherein said first and second frequency radiating and receiving members comprise a housing assembly encompassing said matching and isolation means, said coupling means, and said band matching network; said first and second radiating members being joined together by a non-conductive support member. 